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A. and M. College, Mississippi. 


The ant, Tapinoma sessile Say, a common and widely 
distributed North American species, has been known to ento- 
mologists since 1836, yet it has not been mentioned in literature 
as an economic species until within comparatively recent 

The writer first became aware of the ant as a house pest 
in 1921. Its importance as such was scarcely recognized by 
hirjri until 1924 and 1925 when he found this species to be the 
most important of all house infesting ants at Urbana, Illinois. 
The ant was found in houses in nearly every block investigated 
and in some blocks as high as 80 to 90 percent of the homes 
were infested. Inquiries concerning the relative importance, 
the biology, and the control of this ant were then sent to 
entomologists in all sections of North America. Replies 
received in response to the questionnaries showed the ant to 
be a house infesting species in the following localities: California, 
Nevada, District of Columbia, Maryland, Tennessee, and 
Mississippi. The ant is very probably a pest in a number of 
localities from which no reports are available. In California 
this ant appears to be an especially serious house pest. Essig 
in a letter stated that 50 percent of the trouble from house 
infesting ants in the western section of that state was due to 
this one species. 


This ant passed for many years without a common name 
until Essig named it, the odorous ant, because of the unpleasant, 

*An abstract of a thesis submitted in partial fulfillment of the requirements 
for the degree of Doctor of Philosophy in Entomology in the Graduate School of 
the University of Illinois, 1927. 

(Contributions from the Entomological Laboratories of the University of 
Illinois, No. 122. 


308 Annals Entomological Society of America [Vol. XXI, 

nauseating, .Tapinoma-like smell which it produces. This 
rather descriptive name is objectionable in that there are other 
Dolichoderinid ants having a similar odor, which might be 
confused with this species. The writer would further restrict 
the name, and call the species, the odorous house ant. In the 
New England and North Central States, so far as the writer 
is aware, there are no other Dolichoderinid house infesting 
ants. In the Southern States east of the Mississippi River 
species related to Tapinoma sessile Say are not common house 
pests, excepting the Argentine ant, Iridomyrmex humilis Mayr, 
an imported species. The writer fully realizes the name is 
still open to objection in that there are a number of Dolicho- 
derinid ants which are bad house pests in the Southwestern 
States; however, for want of a better name the ant will be 
referred to throughout this paper as the odorous house ant. 


The odorous house ant was described by Thomas Say as 
Formica sessilis in the Boston Journal of Natural History, 
Volume 1, page 287 for May, 1836, the description being 
based on Indiana specimens. Say's specimens are now non- 
existent. His descriptions, although possessing some very 
salient characters is too brief and inadequate for an ant which 
is so highly variable in color, size, and pubescence as is the 
odorous house ant. The writer has redescribed the species 
from specimens taken at Urbana, Illinois. He believes that 
the specimens from which he has drawn his descriptions are 
very similar to those of Say's since Indiana and Illinois are 

Below is the synonymy of this species, followed by the 
author's description of the ant. 

Formica sessilis Say, Boston Jour. Nat. Hist., Vol. 1, p. 287 (1836) female and 


Tapinoma sessilis Fred Smith, Cat. Hym. Brit. Mus., Vol. 6, p. 57 (1858). 
Tapinoma sessile Mayr, Verb. Zool. hot. Ges. Wien., Vol. 36, p. 434 (1886); 

Emery, Zool. Jahrb. Syst., Vol. 8, p. 332 (1895), female and male. 
Tapinoma boreale Roger, Berl. Ent. Zeitschr., Vol. 7, p. 165 (1863), female and 

worker; Mayr, Sitz. Akad. Wiss. Wien., Vol. 53, p. 397 (1866), worker. 
Formica gracilis Buckley, Proc. Ent. Soc. Phila., Vol. 6, p. 158 (1866) worker, 

Formica parva Buckley, ibidem, Vol. 6, p. 159 (1866) worker. 

1928] Smith: Biology of Tapinoma 309 

Worker. Length, 2.39-3.19 mm. (Plate XVIII, Fig. 1). 

Head oval, broader behind than in front, with faintly eniarginate 
posterior border, rounded posterior angles and convex sides. Mandibles 
with the teeth almost gradually and uniformly diminishing in size 
from the apex to the superior border, the 3 or 4 apical teeth larger and 
more distinct than the others. Eyes moderately convex, placed at a 
distance from the mandibles equivalent to their greatest diameter. 
Clypeus convex, the anterior border distinctly excised medianly, the 
posterior border broadly rounded and extending for some distance 
between the bases of the frontal carinas. Frontal area obsolete. 
Antennal scapes surpassing the posterior angles of the head by almost 
one-fourth their length. Thorax short and robust, anteriorly narrower 
than the head. Pro-mesonotal and meso-epinotal sutures very distinct. 
Viewed laterally, the pro- and mesonotum together form a rather long, 
gentle arch, which terminates at the meso-epinotal constriction; from 
the latter arises a short but gentle arch, which gradually fuses into the 
straight, oblique, declivous surface of the epinotum. Petiole not 
strongly developed, inclined forward and usually concealed by the 
basal surface of the abdomen which is superimposed upon it. Gaster 
subelliptical, broadest at the base and tapering apically; with four 
distinct segments, the remaining segments concealed; basal surface of 
the gaster with a wedge-shaped impression for the reception of the 

Body minutely shagreened, subopaque and slightly glossy. Mandibles 
and anterior border of head more shining, the former with distinct 
scattered punctures. 

Hairs sparse, light yellowish, erect, confined to the mandibles, 
clypeus, prosternum, coxas, and the ventral surface of the gaster and 
dorsal surface of the fourth segment. Pubescence grayish, fine, yet 
distinct, and closely appressed to the body, giving the body a general 
pruinose tinge. 

Body deep brown to black; mandibles and appendages lighter, 
especially the tibis and tarsi of the legs. 

Dealated Female. Length, 3.75-4.29 mm. (Plate XVIII, Fig. 2). 

Head, excluding the mandibles, subquadrate, about as broad as 
long, widest posteriorly, with rounded posterior angles, faintly excised 
posterior border and subparallel sides. Eyes large, rather convex, 
placed at a distance from the mandibles equivalent to less than their 
greatest diameter. Mandibles and clypeus similar to that of the 
worker. Antennas proportionally stouter than in the worker, the 
scapes surpassing the posterior corners of the head by almost one-fourth 
their length. Thorax short and robust; through its greatest breadth 
about as broad as the posterior region of the head. Mesonotum, 
mesoparaptera and scutellum distinctly flattened dorsally, mesonotum 
laterally with a distinct parapsidal furrow on each side. Basal surface 
of the epinotum short, gently convex, not over one-half as long as the 
oblique, declivous surface, into which it gradually merges. (Wings, 
when present, of the same character as in the male). Scale of petiole 
not highly developed, inclined forward and hidden beneath the basal 

310 Annals Entomological Society of America [Vol. XXI, 

surface of the gaster, which is somewhat superimposed upon it. Legs 
of moderate size, distal ends of each tibia with a spur, that of the pro- 
legs clearly pectinate. Gaster subelliptical, broadest basally .and 
tapering apically, with four distinct segments dorsally, the others, 
concealed; base of gaster with a wedge-shaped depression for the recep- 
tion of the petiole. 

Sculpturing similar to that of the worker. 

Pilosity similar to that of the worker; the anterior border of the 
clypeus with a long distinct hair on each side of the median excision. 
Pubescence yellowish or grayish, according to the light, and longer and 
more distinct over all parts of the body than on the worker, thus giving 
the body a more subopaque, pruinose tinge. 

Body varying from brown to almost black; thorax and appendages 
lighter, especially the latter. 

Alate Male. Length, 3.60-4.44 mm. (Plate XVIII, Fig. 3). 

Head, excluding the mandibles, subquadrate, broader behind than 
in front of the eyes, the posterior border faintly convex, the posterior 
corners subangular. Mandibles with one large apical and several 
subequal denticular. Maxillary palpi 6-segmented, labial palpi 4-seg- 
mented, as in the worker and female. Clypeus moderately convex, the 
anterior border with a faint central excision, the posterior border 
broadly rounded and extending some distance between the frontal 
carinse. Eyes elliptical, very large and strongly convex. Vertex 
with 3 prominent ocelli, the distance between the two ocelli approx- 
imately twice as great as that between one of the lateral and the median 
ocellus. Antennas 1 3-segmented, the scapes surpassing the posterior 
corners of the head by about one-fourth their length. Mesonotum 
large, flattened dorsally, and with .a parapsidal furrow on each side, but 
without Mayrian furrows. Wings sordid gray, thickly pilose, and with 
ciliated margins, the veins yellowish-brown. Anterior pair of wings 
each with a single closed discoidal cell, cubital cell, and radial cell, the 
discoidal cell subquadrate. Epinotum with the base and declivity so 
completely fusing that the limits of each are not definitely discernible, 
the two forming a rather gentle, convex surface. Legs moderate in 
size, the distal ends of each tibia with a spur. Petiole inclined forward, 
but concealed for the most part by the base of the gaster which is super- 
imposed upon it. Gaster elongate elliptical, with a wedge-shaped 
impression at the base for the reception of the petiole. Genitalia 
rather large and prominent, stipites large and subtriangular, the cerci 
each with a tuft of hairs or cilia at their distal ends. 

Pilosity resembling that of the worker and female, but different in 
lacking hairs on the dorsum of the fourth segment, which are here con- 
fined for the most part to the stipites of the genitalia and the cerci. 
Body covered with dense, grayish pubescence, which is most discernible 
on the appendages. In certain lights the pubescence of the body has a 
slight, somewhat subopaque luster. The petiole is free of pubescence 
and is therefore smooth and glabrous. 

Body uniform deep brown to almost black; the mandibles and 
appendages scarcely or not at all paler in color. 

1928] Smith: Biology of Tapinoma 311 


The odorous house ant is a member of the subfamily 
Dolichoderince, which in North America embraces seven genera. 
The ants of this subfamily are characterized (1) by the presence 
of a ventral, slit-shaped, cloacal orifice; (2) by the presence of 
anal glands which produce a secretion having a rotten cocoanut 
or nauseating Tapinoma-like odor; (3) by the presence of a 
single-segmented abdominal pedicel, and (4) by the fact that 
the pupae are not enclosed in cocoons. 

1 The food of the ants of this family is small organisms, 
supplemented by honeydew, and the floral, extrafloral and 
glandular excretions of plants. A number of species are 
important house pests: among these being, the Argentine ant, 
Iridomyrmex humilis Mayr; the odorous house ant, Tapinoma 
sessile Say; and the species, Tapinoma melanocephalum Fab- 
ricius. The Argentine ant is without doubt, one of the worst 
house infesting ants in the world. 

Worker ants of the genus Tapinoma can be distinguished 
from the workers of closely related genera in that the abdominal 
pedicel bears a vestigial scale or petiole, which is overshadowed 
by the base of the abdomen. 

Only three species of Tapinoma are definitely known to 
occur in North America, and all of these except one are native 
species. The following key will suffice for the determination of 
the workers. 


1. Workers small, never measuring more than 1.5 mm. in length 2 

Workers larger, measuring at least 2 mm. or more in length; color varying 

from brown to black, appendages lighter; antennal scapes surpassing the 
posterior corners of the head; most common species sessile Say 

2. Antennal scapes surpassing the posterior corners of the head; head and 

thorax very distinctly brown, mandibles, antennae and legs very pale 

yellowish; imported species melanocephalum Fabr. 

Antennal scapes not attaining the posterior corners of the head; general 
color pale yellow, sometimes, however, with the dorsal surfaces of the 
body brownish; native species, at present only recorded from the coast 
of Florida litorale Wheeler 

A species' which has been passing in literature for sometime 
as Tapinoma pruinosus Roger was described by Roger in 1866 
from Cuban specimens (Tapinoma pruinosum, Roger, Berl. 
Ent. Zeitschr. Vol. 7, p. 165 (1866) ). Wheeler in his bulletin 
on the ants of Cuba (Bull. Mus. Comp. Zool. Harvard, Vol. 54, 
p. 497 1913) has shown that the ants which have been passing 

312 Annals Entomological Society of America [Vol. XXI, 

as Tapinoma pruinosus Roger are really Iridomyrmex pruinosus 
(Roger), a species common to the United States as well as to 
Cuba. The name Tapinoma pruinosus Roger is therefore 
relegated to synonymy and the name Iridomyrmex pruinosus 
(Roger) succeeds it. 

On page 16 of this paper, the writer mentions a species of 
ant which Wheeler described from Massachusetts as Bothrio- 
myrmex dimmocki. Wheeler in remarking about the ant 
mentions the fact that he was very much surprised to find a 
species of Bothriomyrmex occurring in North America as no 
species had been previously recorded for this country. 

According to the opinion of Emery the ant should be 
transferred to the genus Tapinoma (Emery, Bull. Soc. vaud. 
Sci. Nat. Vol. 56, p. 19, 1925). Since the writer does not 
posess Emery's paper he does not know what reasons the author 
gives for such a change. To the writer it would appear that 
Wheeler was correct in placing this species in the genus Bothrio- 
myrmex as the workers which he described had 4 segmented 
maxillary palpi and not 6 segmented as do the species of 
Tapinoma. Wheeler does not mention whether the scale of 
the abdominal pedicel of the workers was distinct or not; if it 
was distinct, then the workers of this species would appear 
unquestionably to belong to Bothriomyrmex, since the scale of 
Tapinoma is vestigial. The writer has followed Wheeler for 
the reasons stated and has therefore not considered dimmocki a 
species of Tapinoma as Emery does. 


Ants collected in the field, were brought to the laboratory 
where they were etherized, counted, and placed in the cages 
for observations. These plaster of Paris cages consisted of 
two small, rectangular, intercommunicating chambers which 
were covered by a small pane of glass upon which was a heavy 
piece of carboard. The glass and cardboard not only pre- 
vented the ants from escaping, but held in the moisture and 
made the cages' dark. Food, consisting of nuts, meats, cooked 
eggs, honey, and sugar, was placed in one of the compartments 
of the cage as needed. Since the food would quickly mold it 
was necessary to change it every other day. Observations on 
the number of eggs laid from day to day and on the develop- 

1928] Smith: Biology of Tapinoma 313 

ment of the ants were recorded and compared with field observa- 

In computing the development of the brood, it was necessary . 
to assume that the first eggs laid were the first to hatch, and 
that the first to hatch, were the first to pupate, etc. This 
method, though open to some objections, is the only practical 
means of ascertaining the life history of so complex a social 
insect, inasmuch as it is constantly moving its eggs and brood 
or even at times devouring them. 


Indoors in apartment houses, single residences, green- 
houses, and other places where the temperature is optimum, 
the workers " are active the year around, and very probably 
breeding operations also take place continuously. Due to the 
inaccessibility of such nests, no examinations could be made to 
determine whether development of the brood was taking place 
or not. Dealated females that were brought to the laboratory 
in late fall and kept at a temperature of 70 degrees Fahrenheit, 
or above, laid a few eggs, which took from twenty-two to 
twenty-six days to hatch, and the larvag developing from, these 
eggs made no satisfactory growth until spring. 

Outdoors, on the other hand, the odorous house ant passes 
the winter as workers, dealate females, and partly grown larvse. 
Workers began foraging as early as March 7th. Egg laying 
and uniform development of the brood were continuous pro- 
cesses from late April till cold weather, approximately Novem- 
ber 1st. After a dormant period from November till April, 
the partly grown larva? appeared as workers during April, 
thus requiring six to seven months for their complete life history. 
For eggs laid from April to June, development of the workers 
took place in from five to nine weeks. For eggs laid from June 
to September development proceeded even faster than this, 
requiring only six to seven weeks. No observations were made 
on the development of the males and females. 

Alate females have been observed by the writer and others 
to appear at various dates ranging from June 17th to early 
July, and males have been noted from June 10th to July 9th. 
From the data available it appears that the males emerge a 
short time before the females. Mating is believed to take 
place both inside the nest and outside of it. That mating may 

1928] Smith: Biology of Tapinoma 315 

nests independently, but the writer has not been so fortunate 
as to observe this. That young females of the current season 
begin egg laying soon after fertilization has been proven by the 
writer who kept such females in artificial nests and has obtained 
eggs from them. 

Since the breeding season lasts from April to November and 
since the average time required for the development of the 
worker in summer is seven weeks, four to five generations a 
year is postulated. 


The egg of the odorous house ant is subelliptical in form, 
pearly white in color, lustrous, and without markings. It 
measures .24 by .39 mm. The egg membrane is thin and 
easily ruptured. It is also of such a sticky nature that one 
egg easily adheres to another. In the process of incubation the 
egg gradually loses its luster, becomes more opaque, and 
eventually the form of the developing embryo can be dis- 
tinguished. Incubation requires from eleven to twenty-six 
days according to the season of the year (Fig. 1). 

The freshly hatched larva is scarcely larger than the egg. 
As the larva grows its head becomes recurved ventrally, and a 
peculiar protuberance can be noted on the superior surface of 
the caudal end of the body. The body of the larva is distinctly 
segmented and also somewhat yellowish in color. Beneath the 
integument are small, scattered, white particles, probably 
excretory products. When full grown the larva is rather plump, 
being less distinctly segmented dorsally. The meconium is now 
quite apparent. The head of the larva appears even more 
recurved than formerly, and the caudal protuberance is very 
clearly evident. The larva now measures .72 by 1.74 mm. 
The larval stage occupies from thirteen to twenty-nine days 
(Fig. 2). _ 

The prepupa is an almost exact replica of the full grown 
larva except that the meconium is not evident, it having 
been cast out just before the larva went into this stage. The 
body is robust and very plump. The integument soon accquires 
a much wrinkled, dry appearance. The prepupa measures 
about 1.8 mm. in length. The prepupal stage requires from two 
to three days. 


'Annals Entomological Society of America [Vol. XXI, 

The worker pupa when first formed is naked, white, .and 
destitute of any color markings. It measures from 1.82 to 
. 2.29 mm. in length. The head is directed ventrad, and the 
appendages are borne very close to the ventral surface of the 
body as in the usual manner. The eyes of the pupa begin to 
show a faint brown in color in from two to three days, and in 
from six to nine days not only are the eyes black but the mandi- 
bles are brown and the body has accquired a sordid yellowish 
tinge, the gaster being more infuscated and the head less so. 
The pupal stage lasts from eight to twenty-five days, averaging 
in midsummer about fourteen days (Fig. 3). 


The Maximum, Average, and Minimum Time Required for the Workers to 
Develop from Egg to Adult at Various Seasons of the Year. 














April- June Egg Stage 





*Larval Stage 





Prepupal Stage 

Pupal Stage 





Total Egg- to Adult. . . . 




July-September Egg Stage . 





Larval Stage 





Prepupal Stage 





Pupal Stage . . .... 




Total Egg to Adult. . . . 




Three days after emergence the gaster of the callow is 
deeply infuscated, the head less so, and the thorax least of all. 
The time required for the callow to attain full color in the life 
history cages has ranged over wide limits, usually averaging 
from less than a week to more than three weeks. 


Very little informations was obtained on the length of 
adult life of the various castes. One female was kept eight 
months,- the longest period observed, and was then accidentally 

*This is the time required for the combined larval and prepupal stages. 

1928] Smith: Biology of Tapinoma . 317 

killed by crushing. Many of the females brought in from the 
field died in a period of a few weeks to several months. Death 
in many cases was due to unsatisfactory cage conditions, such 
as the development of mold, etc. Workers appear to be as 
hardy as females and lived equally long. In cages the males 
on the other hand, are very short-lived, perishing within a week 
or ten days. During confinement they seemed to have ex- 
hausted themselves by running nervously about. Under natural 
conditions the females probably live a number of years, as do 
the workers, whereas the males perish within a few days after 


The hardiness of the ants is most remarkable. On a number 
of occasions the writer has accidentally broken off appendages, 
or even crushed the bodies of the female and workers, yet these 
specimens lived and appeared to be little affected by the injuries. 
Some females with considerably crushed abdomens have laid 
eggs in spite of their injuries. In one case, two dealated 
females without food or water, survived confinement in a jar for 
a period of over two months. 


Tapinoma sessile Say is remarkable in that there are so 
many dealated females in each colony, in some nests as many as 
two hundred, all apparently taking part in brood production. 
The females, although considerably larger than the workers, 
are not so much so as in other species. Females kept in life 
history cages over a considerable period of time have laid only 
a very small number of eggs. Sometimes an individual has 
laid as many as twenty to thirty eggs a day, but when an egg 
count was kept over a long period of time it was found that the 
total number of eggs produced by each female was compara- 
tively small; some averaged not over .03 eggs a day, whereas 
the most prolific layers averaged only 1.78 eggs a day. Assum- 
ing that a female begins egg laying in April and lays 1.78 eggs 
per day up to the first of October, she will have laid only 350 
eggs, a very small number. Although the records mentioned 
above were obtained under artificial conditions, the writer 
believes they closely approximate those in nature. The Small 
size of the females and the great number in each nest very clearly 


Annals Entomological Society of America [Vol. XXI, 

indicate that the females are individually not large egg layers, 
and that the flourishing condition of the colony is due to the 
combined output of many females (Table 2). 


Egg laying by the workers has been observed on three 
different occasions, indicating a not uncommon habit of this 
caste. A number of workers without a female, which were 
confined in a cage on May 7th, laid twenty-one eggs by the 


The Total Number of Eggs Laid by Each Female, the Number of Days Each 

Female Was Kept in Confinement, and the Estimated Number of 

Eggs Produced a Day by Each. 


Date Installed 
in Cage 

Date Cage 

Total Number 
of Eggs 

Average No. 
Eggs per Day 



April 9 
April 13 
April 13 

April 30 
April 29 
May 25 

44 . 



April 26 .... 

May 26.. 




June 11 .... 

December 31. . 




June 22 
August 22 
September 5.. . 
November 28 

July 23 
February 6.. . . 
September 19.. 
July 8 . . . . 





November 28. 
December 11. 

May 1 
April 17 




December 11.. 

July 28 



14th of May. These eggs failed to hatch since the workers 
died before the eggs had an opportunity to develop. Whether 
more than one worker was laying is not known. 

The most complete record is that of Cage 9 in which seven- 
teen workers were confined on May 6th. Between this date 
and May 19th they laid a total of forty-five eggs. On May 31st 
small larvae were observed for the first time and on July 10th 
a prepupa appeared, which was almost immediately destroyed 
by the ants before it had a chance to pupate. July 13th 
another prepupa appeared which met a similar fate. Judging 
from the size of the prepupas the writer feels that if these had 
been allowed to pass into the pupal and adult stages they 
would have formed workers. Although this is somewhat con- 
trary to general expectation it is by no means impossible or 

1928] Smith: Biology of Tapinoma 319 

improbable, for Tanner and Reichenbach, experimenting with 
other species of ants, have succeeded in rearing worker ants 
from worker eggs. The writer believes that the workers of 
Tapinoma sessile Say and other ants lay eggs more frequently 
than is usually supposed and that the eggs may at times develop 
into castes other than males. 

A number of writers contend that when workers lay eggs, 
the brood developing from these eggs take longer to reach 
maturity than the brood reared from female eggs. From the 
present data it would appear that their contention is correct. 
With some of the eggs just mentioned the incubation period 
was twenty-three days, and the larval stage forty-one to forty- 
two days. If three days be allowed the brood for the pre- 
pupal, and fourteen days for the pupal stage (the time required 
by the brood reared from female eggs) then it would have taken 
the workers from eighty-one to eighty-two days to attain 
maturity, or a period of eleven to twelve weeks as compared 
with five to nine weeks for workers produced from female eggs. 

Superficially the eggs of the workers appeared larger and 
more elongate than those laid by the females, but the writer 
cannot be sure of this statement for he did not measure or 
otherwise carefully study the eggs, due to their scarcity and the 
fact that he was anxious to have them incubate successfully. 


Probably no ant surpasses the odorous house ant in the 
diversity of its nesting sites. These ants nest in the soil beneath 
stones, boards, leaves, or other rubbish; under the bark of 
rotten logs and stumps; and also in cavities in the stems of 
elder (probably those made by the caterpillar, Achatodes zece 
Harris). Sturtevant found the odorous house ant nesting in 
the galls made by the wasp, Amphibolips confluens Harris 
that were lying on the ground beneath an oak tree. Essig 
stated in a letter that the ants nest in bird's nests, rubbish, and 
trees. In addition the writer has found them nesting in houses 
in Urbana, Illinois. The type of soil or the altitude has ap- 
parently little to do with the choice of their nesting sites. 
The ants have been found to nest all the way from sea level to 
heights of over 10,000 feet, and from nests located in boggy or 
swampy localities to sandy areas along the sea coast or to 
higher and drier locations inland. A study of the nesting sites 

320 Annals Entomological Society of America [Vol. .XXI,. 

of this species has revealed two facts: (1) their lack of perma- 
nency; and (2) their shallowness. Some of the nests are located 
at the surface of the soil or only slightly beneath it. The nests 
are most commonly found in the soil beneath stones, rubbish, 
boards or any such refuse. 


The odorous house ant is evidently acclimated to a wide 
range of temperature and humidity, since it is distributed from 
Canada to Mexico. At Urbana, Illinois, the workers have not 
"been noted foraging outdoors at a temperature below 50 degrees 
Fahrenheit. At this temperature the ants appeared as if 
numbed by the cold and moved at a slow gait, as compared 
with their usually quick method of scurrying along. Workers 
however, have been observed to enter refrigerators and get 
into the ice compartments where the temperature must certainly 
have been below" 50 degrees Fahrenheit. The ants do not like 
to cross water and if possible avoid doing so ; but once in the 
water, due to the lightness of their bodies, they can float on 
the surface film, and in their violent struggles usually manage 
to propel themselves to one side and crawl out. Many colonies 
have escaped from the writer by crossing a slow stream of water 
which surrounded their nest. Rain, by washing their favorite 
food, honey-dew, from the foliage of plants, ' often causes the 
ants to invade homes; in fact, many housekeepers state that 
the ants are worst immediately after a rain. The writer has 
seen workers foraging in his yard when a wind storm was in 
progress, which was so violent as to blow aphids from trees. 
The aphids referred to were the box elder louse, Periphyllus 
negundinis Thos. That the ants can stand considerable heat 
is shown by the fact that they often construct nests under 
small piles of leaves or in compost heaps where the temperature 
is undoubtedly very high. 


Few ants excel the odorous house ant in its honey-dew 
loving habits. It is an aphidicolous and coccidicolous species 
par excellence and deserves to be ranked with such ants as the 
corn field ant, Lasius niger. var. americanus Emery, the honey 

1918] Smith: Biology of Tapinoma 321 

ant, Prenolepis imparis Say, and other such honey-dew loving 

The writer has very commonly witnessed the workers of 
this species stroking with their antennae, the box elder louse 
and obtaining from them the much sought honey-dew. The 
ants also showed a keen interest in mealy-bugs, especially 
individuals of the species Pseudococcus maritimus Ehrh. which 
they attempted to pick up and carry away when the .writer 
sought to take specimens of the mealy bugs from the trunk of 
box elder trees. The workers of the odorous house ant may 
also distribute plant lice and other honey-dew excreting forms. 
On two occasions they have been seen carrying live box elder 
lice in their mouths and also a species of Macrosiphum, common 
on raspberry. A list of some of the insects with which this 
ant has been found associated is given below : 

Aphididce: Periphyllus negundinis Thos. on box elder; 
Chaitophorus viminalis Monell on American aspen and quaking 
aspen trees; Aphis viburnicola Gill, on Viburnum opulus L. ; 
Aphis sp. on Englemanns Ivy; Anuraphis cardui Linn, on 
plum; Aphis sp. on burdock; Aphis rumicis Linn, on Viburnum 
opulus L. ; Aphis helianthi Monell on sunflower; Neothomasia 
populicola (Thos.) on cottonwood; Myzus cerasi on cherry; 
Macrosiphum solanifollia Ashm. on rose and raspberry; 'Aphis 
pseudobrassicce, Davis on turnips and Chaitophorus delicata 
Walker on an undetermined host. 

Coccidce: Lecanium sp. on box elder; Kermes sp. on water 
oak; Chionaspis furfur a (Fitch) on apple; Saissetia hemisphcerica 
(Targ.) on lemon and olive; Coccus hesperidum Linn, on orange; 
Pseudococcus citri (Risso) on Dracaeena plant, the rice paper 
plant, lemon and coleus; and Pseudococcus maritimus (Ehrh.) 
on box elder. 

Membracidce: Entylia sinuata Fabr. on sunflower. 


During the period of two years devoted to the study of 
this ant, the writer failed to observe any fight or animosity on 
the part of Tapinoma sessile Say toward any other native 
species which it encountered. The odorous house ant is 
extremely common at Urbana, Illinois, and its nests are situated 
near those of other species, yet the ants do not seem to fight. 
When the odorous house ant. encounters another species, each 

322 Annals Entomological Society of America [Vol. XXI, 

seems to sense the other's presence and they therefore avoid 
one another. On one occasion the odorous house ant and 
the corn field ant, Lasius niger var. americanus Emery, were 
found foraging in a kitchen at the same time, yet the two 
species did not intermingle. The tiny thief ant, Solenopsis 
molesta Say, and the ant, Strumigenys pulchella Emery, have 
been found to live with this ant in what appeared to be com- 
pound nests. The tiny thief ant is known to feed on the brood 
of other species of ants and the species of Strumigenys are sus- 
pected of the same habit. 

King (1897) has found mixed colonies of the odorous house 
ant and the following species: Formica fusca var. subsericea 
Say, Lasius flavus subsp. nearcticus Wheeler, and Lasius niger. 
var. americanus Emery. 

Wood worth (1910) appears to be the only observer who has 
seen the odorous house ant in conflict with another species; 
namely, the ubiquitous Argentine ant, Iridomyrmex humilis 
Mayr. The latter species is noted for its pugnacity toward all 
ants it encounters except a few small species such as the tiny 
black ant, Monomorium minimum Buckley, and Pharaoh's ant, 
Monomorium pharaonis Linn. Wood worth has the following to 
say concerning the conflicts between the Argentine ant and the 
odorous house ant : ' ' This odor is produced by a liquid secretion 
(speaking of the ejections from the anal glands) which can 
be ejected from the abdomen as an appreciable drop, and 
which is used in its contest with the Argentine species. As 
long as the supply of the secretion lasts the Tapinoma has no 
difficulty in keeping the Argentine ant off, but after having 
put four or five Argentines out of the combat in this way 
finally the Tapinoma is put to rout and the Argentines are 
invariably victorious, because they always attack in sufficient 
numbers. We have observed many battles between these 
species and the Tapinoma is always driven away from its feeding 
ground and its home despoiled." 

If there is any animosity exhibited by individuals of one 
colony of Tapinoma sessile Say towards those of another colony, 
the writer has not witnessed it. He has mixed colonies arti- 
ficially in the laboratory and has also seen alien colonies combine 
of their own accord. 

Wheeler (1916) described a species of ant, Bothriomyrmex 
dimmocki, from Massachusetts, which he states may be a 

1928] Smith: Biology of Tapinoma 323 

temporary parasite on the odorous house ant, like its cogener, 
B. atlantis Forel, of Tunis is on Tapinoma nigerrimum Nyl. 
The female of B. atlantis Forel after descending from her 
nuptial flight is pulled into the nest of T. nigerrimum Nyl., by 
the workers of that species. She soon crawls on the back of 
the nigerrimum female and decapitates her. After the death 
of the nigerrimum female, the workers of that species accept 
the B. atlantis female and rear the brood she produces. Eventu- 
ally all the nigerrimum workers die and the colony then becomes 
a pure one of B. atlantis. 


In the nests of the odorous house ant, Mann (1911) has 
found the little cricket, Myrmecophila oregonensis Bruner, and 
also a little wingless wasp, Isobrachium myrmecophilum Ashm. 
"Ashmead states that the genus (Isobrachium) is parasitic 
upon the ants or other myrmecophilous Coleoptera," according 
to Mann who writes further, "the latter being so rare in the 
nests of Tapinoma, it is probable that Isobrachium is a parasite 
on the ant itself." The crickets, M. manni Schimmer and 
nebracensis Lugger, have also been taken in the nests of this ant. 

The following species of Coleoptera, most of which are rove 
beetles (Staphylinidce) , have also been taken from the nests of 
the odorous house ant by Mann, Wheeler, and others: Zyras 
tapinomatis Mann, Myrmoecia lugubris Casey, Nototaphra 
lauta Casey, Connophron longipenne Casey, and Myrmedonia sp. 

The writer has found in the nests of the odorous house ant 
an unidentified species of spring tail (Collembola), termites 
(Isoptera), and sow bugs, Armadillidium vulgare (Latr.). In 
the laboratory a species of book lice thought to be Troctes 
divinatoria (Muller) appeared in the cages and fed on the' 
dead bodies of the ants and other refuse. Neither were the 
ants observed to attack the lice nor the lice to trouble the ants. 


The only animals known to feed on the odorous house ants 
are birds and toads. - A winged male of this ant was taken 
from the stomach of a toad, Bufo sp., at Anna, Illinois, by a 
member of the Illinois State Natural History Survey. The 
following list of the species of birds known to feed on the 

324 Annals Entomological Society of America [Vol. XXI, 

odorous house ant was sent to the writer by the United States 
Bureau of Biological Survey: the pigeon hawk, Falco columbarius 
Linn; the American magpie, Pica pica hudsonia (Sabine) ; the 
Bartramian sandpiper, Bartramia longicauda Bechet; the chim- 
ney swift, Chaetura pelagica Linn. ; the crow, Corvus brachy- 
rhynchos brachyrhynchos Brehm; and the red shafted flicker, 
Colaptes cafer collaris (Vigors). Bryant (1914) mentions that 
the western meadowlark, Sturnella neglecta neglecta Audubon, 
feeds on this species of ant and the writer has observed the Eng- 
lish sparrow, Passus domesticus Linn, doing the same thing. 


The odorous house ant not only visits plants for the purpose 
of attending insects but for the purpose of visiting also the 
floral and extrafloral nectaries and other glandular excretions. 
The workers have very commonly been seen lapping up exudates 
on the buds of peonies. This habit apparently causes the buds 
to dry out to such an extent that the flowers developing there- 
from are smaller and in many cases malformed. Dietz (1926) 
states that the black lawn ant, Formica fusca var. subsericea 
Say, can spread peony bud wilt by means of the workers crawl- 
ing from infected to non-infected buds, while visiting the buds 
for the much sought exudates. If this be true in case of the 
lawn ant, it should also apply for the odorous house ant, for 
it, like the lawn ant, is a persistent visitor of peony buds. 
Davis of New York (1922) states that he has seen workers of 
this species visiting the glands at the base of the leaves of 
Populus grandidentata Michx. The writer has seen this ant in 
attendance on the glands of castor bean plants. 

During 1926 the writer found a fungus, Laboulbenia formi- 
carium Thaxter, infecting several species of ants in Urbana, 
Illinois, namely: Formica fusca var. argentea Wheeler, F. 
neogagates Emery; Lasius niger var. neoniger Emery, and F. 
pallide fulva schaufussi var. incerta Emery. Although the 
odorous house ant was present on the same blocks as the 
species mentioned above, this ant was not found to be infested 
with the fungus. 

In the laboratory, colonies of the odorous house ant were 
'often choked out by luxuriant growths of the bread mold, 
Rhizopus nigricans Ehrh., and a species of Aspergillus. These 
molds arose from foods that were allowed to remain in the 

1928] Smith: Biology of Tapinoma 325 

cages too long, thriving best where there was considerable 
excess moisture. The writer did not find the ants outdoors to 
be affected by any sort of fungus and he doubts if they ever are. 


The food of the odorous house ant under normal conditions 
is largely honey-dew, supplemented by the flesh of organisms 
and the juices of fruits. The ants are also very fond of the 
floral and extrafloral secretions of plants. In the laboratory 
cages the ants occasionally fed on their brood. It is presumed 
that under outdoor conditions this seldom, if ever, happens. 

When the ants enter houses they are almost omnivorous but 
seem to show a slight preference for sweets. In a number of 
homes in Urbana, Illinois, the ants have been known to cut 
through paraffine in order to reach jelly and preserves in 
containers. They have been noted to infest the following 
foods: honey, sugar, preserves, pies, custards, marmalades, 
cooked and uncooked beef, fish, raw and fried liver, boiled and 
mashed potatoes, stewed prunes, cheese, milk, ice cream, and 
ripe fruits. 


The colonies of this ant show a wide variation in size, perhaps 
due to their age. The smallest colony observed contained only 
four dealated females and about one hundred workers. The 
largest colony noted was estimated to contain about ten thou- 
sand individuals, including brood and adults. An average 
colony may be expected to contain between two thousand and 
five thousand specimens. 

One of the most striking characteristics of the colonies of 
this ant is the unusually large number of dealate females, all of 
which no doubt take part in reproduction. The females, 
unlike those of the honey bee, are most amiable toward one 

From observations that have been made it is believed that 
the sexed-forms are not produced in any but the older and 
stronger colonies. Although many nests have been examined 
sexed-forms have been found only in the larger and more 
flourishing colonies, which were very probably from four to 
five years of age (Table 3). 


Annals Entomological Society of America [Vol. XXI, 


The workers of the odorous house ant are strikingly slender 
and graceful in appearance. When alarmed they run with a 
rapid, erratic, jerky sort of pace and oftentimes with the 
caudal end of their abdomen slightly elevated. When a nest is 
disturbed it is only a few seconds until the ants are running 
everywhere in a somewhat helter-skelter manner. 

The workers are splendid foragers, who seek food by night 
as well as by day. Very seldom are they seen foraging singly 
but are ordinarily observed trailing along in a file from their 


The Size of the Colonies and the Types of Castes and Immature Stages in the 
Nest at Various Periods During the Year. 

Total No. 














Apr. 1-25 




Apr. 8-26 

. p 



Apr. 12-26 




Apr. 25-26 





June 1 1-25 






June 6-26 









June 27-25 









Aug. 22-25 






Sept. 5-25 






Nov. 10-25 






x Form present. 
* Alate and Dealate Females. 

NOTE. Workers are not mentioned in Table because they are present all the 
year and comprise the largest percentage of individuals in the nest. 

nest to the source of food supply. The ants seldom have to 
travel over thirty to fifty feet to find food, and for this reason 
their trails are generally not long. Their foraging activities 
take them into every conceivable sort of place, such as garbage 
cans, commodes, dirty linens, pantries, sinks, refrigerators, and 
other places too numerous to mention. Like their cogeners, 
the Argentine ants, the odorous house ants are prying little 
busybodies, eternally poking their antennas into everything. 

1928] Smith: Biology of Tapinoma 327 


When hungry the ants eat very greedily. The writer found 
that a worker will feed from three to five minutes before she 
seems satisfied. During this time her gaster gradually en- 
larged until the chitinous segments stood out like small islands 
between the intersegmental membranes. 

Workers have often been observed regurgitating food to the 
female or to other workers. They also feed their larvae in this 
manner but never with solid particles as do some of the primitive 


The workers are good nurses as well as foragers. Whether 
there is any particular division of labor among them, the writer 
does not know, since the individuals are practically all the 
same size (monomorphic) and indistinguishable. Recently 
emerged individuals (callows) show considerable interest in 
the brood and will attempt to pick up the brood and carry it 
away when the nest is disturbed. The dealated females seem 
to- show little interest in the brood, leaving their care to the 
workers, when these are present in sufficient numbers. The 
workers show considerable attention to the female and to the 
brood, around which they cluster. Since the pupae of this 
ant has no cocoon covering it, the assistance of the worker for 
its removal at emergence is not necessary. The writer has, 
however, noted a worker removing the meconium from a larva 
which was preparing to enter the prepupal stage. Workers 
are continually seen licking the brood, the females, or other 


The writer wishes to express his gratitude to Dr. C. L. 
Metcalf for his unfailing interest and guidance in the work and 
in the preparation of this paper. He is also grateful to Dr. 
W. P. Hayes, Dr. R. D. Glasgow, and Dr. W. V. Balduf for 
their valuable aid and many helpful suggestions. The writer 
is also indebted to the United States Bureau -of Biological 
Survey and the Illinois State Natural History Survey for 
furnishing valuable data, and to Dr. W. E. Britton, Mr. J. R. 
Horton, and Mr. S. A. Rohwer for the loan of specimens. 
Mr. P. W. Mason kindly determined the plant lice for the 

328 Annals Entomological Society of America [Vol. XXI, 


1. Tapinoma sessile Say, a native North American ant, is 
of considerable economic importance as a house pest not only 
in Urbana, Illinois, but in localities in California, Nevada, 
District of Columbia, Maryland, and Mississippi. 

2. The synonymy and a redescription of the species is 
given in this paper. The immature stages of the ant are also 

3. The common name, the odorous house ant, is applied to 
the species for the first time. 

4. The ants overwinter outdoors as dealate females, 
workers, and larvae. Workers begin foraging as early as 
March 7th. Egg laying and the uniform development of the 
brood begins in late April and continues until cold weather in 
the fall or approximately November 1st. The overwintering 
larvas attain maturity in April, having required from six to 
seven months to attain maturity. From April through June 
workers can be produced in from five to nine weeks, whereas 
during the period July through September they require only 
six to seven weeks to attain maturity. Four to five generations 
of workers a year are postulated. 

5. Alate females were observed at various dates ranging 
from June 17th to early July. Males appeared from June 10th 
to July 9th. Only large and strong colonies seem capable of 
producing sexed-forms. Mating probably takes place both in 
and outside of the nest. 

6. Colonies range from a hundred to ten thousand indi- 
viduals. The average colony contains from two thousand to 
five thousand individuals, many of which are dealated females; 
one colony contained' over two hundred dealated females. 

7. Some of the workers lay eggs. The brood reared from 
such eggs attained the prepupal stage before they were eaten 
by the workers. It is believed that if they had attained maturity 
the adults would have been workers. Development of -brood 
from worker eggs apparently takes longer than the develop- 
ment of brood from female eggs. 

8. The ants show a wide diversity in their nesting habits. 
Nests have been found in houses; under the bark of logs and 
stumps; in galls on plants; in stems of plants; under debris; and 
in the soil. 

1928] Smith: Biology of Tapinoma 329 

9. The species is apparently eurythermal in disposition as 
it is found throughout most of North America from the sands of 
the seashore to heights of over ten thousand feet and from 
boggy locations to perfectly dry inland spots. Workers have 
been seen foraging at temperatures as low as fifty degrees 

10. The natural food of the ants is honey-dew, supple- 
mented by the flesh of organisms. In houses they feed on 
fruits, vegetables, meats and sweets, but seem to show a prefer- 
ence for sweets. 

11. A list of the species of plant lice, scale insects, mealy- 
bugs, tree hopper, etc., which they are known to attend is given 
in this paper. 

12. A number of beetles, wasps, crickets, spring tails, 
termites, book lice and other insects have been found living in 
association with the ants. 

13. A species of toad and eight species of birds are known 
to feed on the ants. 


Bryant, H. C. 1914. Univ. of Cal. Pub. Zool., 11: 21-24. 

Davis, W. T. 1922. Bull. Bklyn. Ent. Soc., 17:2. 

Dietz, H. F. 1926. Insect Pest Survey, 6: 122-123. 

Doten, S. B. 1910. Nev. Agr. Expt. Sta. Bull., 73.5: 43-44. 

Emery, C. 1912. Genera Insectorum, 137: 40. 

Essig, E. O. 1926. Insects of Western North America. McMillan Co., N. Y., 

pp. 863-864. 

King, G. B. 1896. Entomological News, 7: 169. 
Mann, W. M. 1911. Psyche, 18: 29. 
Reichenbach, H. 1902. Biol. Centrabl., 22: 461-465. 
Say, Thos. 1836. Boston Jour. Nat. Hist., 1: 287. 
Tanner, J. E. 1892. Trinidad Field Naturalist's Club, 1: 123-127. 
Wheeler, W. M. 1910. Ants, Their Structure, Development and Behaviour. Co- 
lumbia Univ. Press, N. Y., pp. 45. 

1913. Bull. Mus. Comp. Zool., Harvard, 54: 497. 

1915. Bull. Amer. Mus. Nat. Hist., 34: 417-418. 
Woodworth, C. W. 1919. Univ. Cal. Publ., 207: 70-71. 



Marion R. Smith 

Tapinoma sessile Say. 
Fig. 1. Worker, greatly enlarged. 
Fig. 2. Dealated female, greatly enlarged. 
Fig. 3. Alate male, greatly enlarged.